Tides are the regular fluctuations in the mean sea level that are caused by the gravitational attractions of the Moon and Sun. Tides are usually the mean tidal height denoting the relatively short-period, astronomically induced vertical changes in the sea surface (exclusive of wind-induced waves and earthquake-caused tsunami). Another useful term is tidal current that refers to accompanying periodic horizontal movement of the ocean water.
Tides are influenced by many factors including astronomical, non-astronomical, or random ones. The astronomical factors include two types of forces responsible for producing tides. One is the force of gravitation exerted by the Moon and Sun upon the Earth. The other is the centrifugal force produced by the revolution of the Earth and Moon (and the Earth and Sun) around their common center-of-mass.
The net effect exerted by the Moon and Sun on the Earth depends upon their relative positions. One way to describe the relative positions of the Earth, Sun, and Moon is using the phases of the Moon. The Sun always illuminates one half of the Moon facing the Sun, except for lunar eclipses. When the Sun and Moon are on opposite sides of the Earth, the Moon appears “full” to us. When the Moon is between the Earth and Sun, it appears dark, a “new” Moon. In between, the Moon's illuminated surface appears to grow from a new Moon to a full Moon, and then decreases to the next new Moon. When the Moon is at new or full phases, the gravitational attractions of the Moon and Sun synergistically induce greater-than-average tides, known as spring tides. When the Moon is at first or third quarter phases, the gravitational attractions of the Moon and Sun partially counteract each other so as to induce high tides that are lower than average and low tides that are higher than average. Such tides with diminished range are called neap tides.
The non-astronomical factors such as configuration of the coastline, local depth of the water, ocean-floor topography, and other hydrographic and meteorological influences may play an important role in altering the range, the interval between high and low water, and the times of arrival of the tides. For example, friction between the water and ocean floor slows the movement of the tides; land masses impose a barrier to the progress of tidal water; and topography on the ocean floor provides a restriction to the forward movement of tidal water. All these factors may delay arrivals of tides for up to 3.5 hours.
Unpredictable random factors may have significant effects on the tides. Such factors include flood, winds, rain, freshwater runoff, and other short-term meteorological events. For example, earthquakes may generate tsunami, generating tidal waves that are much higher than normal regular tides.
Information of tidal heights and their arrival times is critically important for a variety of activities including navigation through inter-coastal waterways and within estuaries, bays, and harbors; harbor engineering projects; cruise and container terminal berth allocation and scheduling; provision of information necessary for underwater demolition activities and other military engineering uses; fishery; water-related sport activities; and utilization of hydro-dams as energy generators. Therefore, tidal prediction is of great practical significance.
A considerable amount of effort has been made for tidal prediction so far. Many methods and devices have been proposed for tidal prediction and tidal information display. For example, U.S. Pat. No. 6,226,594 discloses a method and device for calculating a spring tide day. The spring tide day is useful for certain industries, however, it does not predict the daily and hourly tidal height values which are useful for other industries and recreations.
Currently, to make tidal predictions which closely approximate the National Oceanic and Atmospheric Administration (NOAA) predictions one must use the “Harmonic Analysis” method as described in the “Manual Of Harmonic Analysis and Prediction of Tides”, Special Publication No. 98 published by the U.S. Department of Commerce, described in US published patent application US 2003/0167124 A1, [0005]. Since tides are generated essentially by astronomical forces of harmonic nature, it is no surprise that the harmonic analysis is the principal method used in tidal study and prediction.
The harmonic analysis of tides is based upon an assumption that the rise and fall of the tides in any locality can be expressed mathematically by the sum of a series of harmonic terms having certain relations to astronomical conditions. From Special Publication 98 (paragraph 8) “Harmonic Analysis” as applied to tides is the process by which the observed tidal data at any place are separated into a number of harmonic constituents. The quantities sought are known as harmonic constants consisting of amplitudes and phases. Harmonic prediction is accomplished by reuniting the elementary constituents in accordance with astronomical relations prevailing at the time for which the predictions are made.
“Harmonic Analysis” method to predict tidal times and heights for any given locality is complex and labor intensive. It requires tidal observations at one water station over a long period of time, typically 18.6 years. In addition, it requires the use of harmonic constraints and a control file for each location for which the tidal predictions are to be generated. Furthermore, the existing tidal prediction systems are very large and complex. It is not possible to integrate such systems into other IT systems such as cruise and container berth allocation systems that require timely tidal prediction. As a result, the existing tidal prediction systems are not readily available for wide range of industrial applications for real-time tidal predictions. Finally, the prediction accuracy achieved by the existing tidal prediction systems varies in a significantly large range with correctness of specification of numerous parameters including astronomical and non-astronomical ones, as well as local control parameters. If these complex parameters are not defined precisely, which is difficult even for professionals, the tidal prediction accuracy can be miserably low and unacceptable.
Therefore there is an existing need of a tidal prediction system and method that is simple, easy to use, portable, and world-wide applicable. Furthermore, the system and method can provide real-time tidal predictions with sufficient prediction accuracy for various industrial applications. This invention satisfies this need. Other advantages of this invention will be apparent with reference to the detailed description.